Ahh, thanks man. I just tested an acid varnish and that didn't work. I'm guessing then that they want to have the varnishes ward against their opposites, but what would be opposite to acid and electricity? I'll look forward to seeing how they figure that one out.
So right now, Acid sheath is still mage's best friend!
Actually furthermore, acid sheath would still be 'some' good even if greater acid varnishes were applicable to armor, since it'd only be 30 acid soak...one can potentially get 10+1d6 further acid damage out of the spell.